Sound.

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Presentation on theme: "Sound."— Presentation transcript:

2 Characteristics of sound wavesThe motion of the elements of the medium in a longitudinal sound wave is back and forth along the direction which the wave travelsIn transversal wave, the vibration of the elements of the medium are at right angles to the direction of travel of the wave\Sound waves: audible waves, infrasonic waves( earthquake), ultrasonic wave

3 The speed of soundv=√B/ρ;b- bulk modulus of the fluid B=ΔP/(ΔV/V)For a speed of transverse wave on a string v=√F/μThe speed of mechanical wave: v=√elastic property/inertial propertySpeed of longitudinal wave in a solid rod v=√Y/ρ; Y-young’s modulusRelationship between speed of sound and temperature : v=(331 m/s)√T/273K

4 Energy and Intensity of sound wavesThe average intensity T of a wave on a given surface is defined as the rate at which energy flows through surface ΔE/Δt, divided by the surface area: I=1/A(ΔE/Δt), where the direction of energy flow is perpendicular to the surface at very pointSI unit: W/m2I=power/area =P/A

5 The relative intensity of a sound is called the intensity level or decibel level β=10 log (I/Io)The Doppler effect (is associated with sound, but its common to al waves, including light)

6 #1 The observer is moving relative to a stationary sourceThe observer speed: v=0If fs- frequency of the source, λs- wavelength of the source, v- speed of sound in airDuring an interval of time, the observer detects an additional number of wave fronts = vot/λs ; fo=fs+vot/λsfo=fs(v+vo)/v -the frequency heard by the observer ( when moving away: v–vo)

9 Standing wavesThe superposition principle traveling waves move in both direction on the stringStanding wave- if the string vibrates at exactly same frequencyA node- 2 traveling wave have a same magnitude but opposite directions ( no motion on a string)Antinode- midway between 2 adjactent nodes ( the maximum amplitude)All points on the sting oscillate together with the same frequency but different points have different amplitudes of motion

10 The ends of the string must be nodes, because these points are fixedThe distance between a node and a antinode = λ/4There are two segments, so, L=2(λ/4)=λ/2 and λ=2LThe frequency of the vibration:f=v/λ =v/2Lv=√F/μf=1/2L√F/μ fundamental frequency or first harmonic